1. Field of the Invention
The present invention relates to an image pick-up apparatus having high S/N and small image distortion.
2. Related Art Statement
Heretofore, there has been practiced an optical scanning type microscopic image pick-up apparatus in which a light beam is deflected two dimensionally by means of two deflectors to scan a specimen at a high speed with a fine spot, and a light flux reflected by the specimen is transmitted through the two deflectors in the opposite direction and is made incident upon a light receiving element such as a photomultiplier tube to generate an electric signal representing optical information of the specimen. Such an image pick-up apparatus has several advantages that any stray light can be prevented due to the fact that the specimen scanned by the beam spot, an image displayed on a monitor can be inspected, and that brightness and contrast of the displayed image can be electrically adjusted in an easy and precise manner. Therefore, such an image pick-up apparatus can be advantageously utilized in various applications.
As an image sensor there has been also developed a two dimensional solid state image sensor. Usually, the two dimensional solid state image sensor has been used instead of an image pick-up tube onto which an image of a uniformly illuminated specimen is projected by means of an objective lens.
In the known optically scanning microscopic type image pick-up apparatus, since the specimen is scanned by a light beam at a high speed, it is necessary to use the photomultiplier tube having high sensitivity, and therefore the apparatus is liable to be large in size and expensive in cost. Further, it is very difficult to deflect the light beam two-dimensionally at a constant speed to scan the specimen. If the scanning speed fluctuates, there might occur an image distortion and therefore the image of specimen would not be reproduced accurately. Further, since the two dimensional solid state image sensor has a low sensitivity, it is necessary to use a light source emitting high intensity light. Then, the apparatus comprising the solid state image sensor is also liable to be large in size. Moreover, since the definition or resolving power of two dimensional solid state image sensor is relatively low, the definition of the reproduced image could not be made high. Such a definition is too low to apply the image pick-up apparatus to a defect detection system.
Further, in the known image pick-up apparatus, the light source and photodetector could not be used commonly for the reflection type inspection and transmission type inspection. Therefore, when the same specimen is to be observed both in the reflection type inspection and in the transmission type inspection, the specimen has to be first set in reflection type apparatus and then has to be removed to a transmission type apparatus. Therefore, the operation of user becomes very complicated and sometimes it is very difficult to inspect the same part of specimen in both modes. Moreover, there must be provided two apparatuses and this requires large space and high cost.